As the film opens, we are with sniper Bobby Lee Swagger (Mark Wahlberg) and his scout Donny Fenn (Lane Garrison) lying in wait in the hills of Ethiopia, ready to deliver covering fire for a US convoy heading back to base through hostile country. They pass the time with small talk: Donny looks at a photo of his wife, Sarah (Kate Mara). Far below, a lone truck carrying a machine gun in the back speeds towards the American convoy. Swagger takes out the shooter and driver, each with a single shot to the head. It seems like the mission is over as the Americans make their way down the road until a horde of hostile militia appear, firing on the soldiers. Donny relays target information while Swagger systematically shoots and kills numerous hostiles, allowing the US forces to escape.

Protecting the convoy has revealed the sniper’s position, and soon the two snipers are under heavy fire. Back at base, their commanding officer is more concerned about avoiding detection, as the Americans aren’t supposed to be in the country, and Swagger and Donny are abandoned, left to fend for themselves, left for dead. An enemy helicopter begins to strafe their position. Donny is killed. Swagger fires futilely at the helicopter with his sniper rifle until he uncovers a Barret 50 caliber VBM82A3 SASR, and returns fire on the helicopter, bringing it down in flames. As the helicopter explodes, this episode fades, with Swagger, abandoned, and fighting his way home alone.

Three years later Swagger is a private citizen, living in the mountains, a recluse from the world that abandoned him. Unshaven and long haired, he lives alone; his only companion his dog, trained to open the fridge and take out a cold beer for Bobby Lee as he returns to his cabin. Sharing a slurp of the beer with his dog, Swagger turns on his PC and the Internet, looking at news of a world that mostly has him shaking his head. Cutting away to a military office, wheelchair-bound Michael Sandor (Rade Serbedzija), Colonel Isaac Johnson (Danny Glover), Jack Payne (Elias Koteas), and Louis Dobbler (Jonathan Walker) are planning an op: Sandor recommends Swagger, and they discuss his past… this lost soul, covert-ops hero now turned loner, seems perfect for their needs. Bouncing up the woodland track, Johnson and his men drive out to meet Swagger.

Alerted by his barking dog, Swagger is alerted as the men approach his cabin. Johnson introduces himself to Swagger, flaunting his own Medal of Honor. Tension mounts, as Swagger is not interested in talking, and when Payne tries to lure the dog to him, Swagger warns him off. Tension escalates as Payne reaches slowly down towards his gun and Swagger readies a hidden blade. Johnson calms the situation, convincing Swagger to give him five-minutes. Payne and Dobbler wait outside as Johnson explains their presence: they have received information about a planned assassination attempt on the president and, with a mole in one of their agencies, they’ve turned for help to Swagger. One of their few intelligence clues is that the assassin’s shot will be taken from over a mile, a shot which few men can make. Still Swagger wants nothing to do with the plan, but Johnson insists. The president will travel to three different cities, and Johnson wants Swagger to travel to each and scout potential places for a sniper. Feelings of patriotism, or perhaps habit begin to change Swaggers mind. Still, as Johnson prepares to leave, Swagger takes a picture of as he admires their truck’s engine. As they drive back down the mountain, Swagger’s professional suspicion is understood by Johnson and his men they know he didnt take a picture of the engine, but of their license plate. But he’s agreed to their plan.

Swagger sets up a can of beef stew and practices the beyond a mile shot, nailing it with complete accuracy. Swagger cuts his hair and trims his beard. As he cleans his guns he tells his dog that he’ll be gone for a couple of days.

True to his word, Swagger scouts each location in turn, reporting back to Johnson that the likely location is Philadelphia. Johnson wants Swagger there to help catch the assassin. Spooling forward to the day of the speech, snipers are everywhere, along with federal agents including Nick Memphis (Michael Pena). Swagger stands in nearby office with Johnson, Payne, and Dobbler, and a pudgy police officer who Payne introduces as Timmons (Alan C. Peterson). Johnson claims the shooter is in a church tower nearby, and says that they will take him down just after the president begins to speak, but Swagger’s eye is taken by the fact that Timmons’ gun is not properly holstered. The president is scheduled to speak immediately after the Archbishop of Ethiopia, who is accepting an award. As the president approaches the stand, Swagger urges Johnson to have his men take down the shooter immediately, but at that moment events lurch forward: the Arch Bishop is shot in the head, and Timmons fires on Swagger, catching him in the shoulder. Swagger falls out of a window, landing hard on a glass ceiling below. Timmons leans out and shoots Swagger in the stomach, driving him through the glass ceiling. As Payne’s team men pack up their things he abuses Timmons for not killing Swagger. They leave the only belongings left behind are Swaggers sniper rifle and a bullet. Payne orders Timmons to finish Swagger off.

Swagger is on the run for his life. He stumbles into Memphis, asking for his help. Memphis draws his gun but Swagger flips him over hard on the ground. He ‘cuffs Memphis to a gate, telling that he was set up and Timmons is in on it. Grabbing Memphis’s gun, Swagger drives off in his car. Timmons catches up to Memphis, and alerts the cops that Swagger stole an FBI car. Now everyone is searching for Swagger, and he drives into a car wash to hide from the helicopters. While his car is being washed, Swagger hops in the back seat and cuts a hole to the trunk, where he grabs a medic kit and tends to his wounds. Speeding out of the car wash he is seen again by the cops and a chase ensues. The back end of his car is smashed by a truck, causing him to spin around and Swagger finds himself directly in front of a line of police officers. Throwing the car into reverse as the cops open fire on him, Swagger drives through a construction site and directly into a lake. The cops find the car, but no Swagger. He is pulled alongside a boat, and makes it underneath a bridge. From there, he hot-wires a truck and takes off. Meanwhile, FBI agents watch a news report of the assassination attempt and of Swaggers escape. They all are not happy that Swagger overpowered Memphis so easily, even though Swagger is highly trained and Memphis is three weeks out of the academy. While meeting with his superior officer and other agents, Memphis tells them what Swagger said to him, but they all say that he didnt hear anything. Memphis will be put up for review. Swagger drives to a store and knocks out the power, then goes inside and buys supplies. Swagger drives to an empty car repair station and makes an IV for himself using the supplies.

Swagger drives all night to Kentucky, where he goes to Sarahs home. Shes startled by him coming by, since shes seen the news about what happened. Sarah lets him come inside, and he apologizes for not coming to meet her after Donny died. She did receive his letter though, along with flowers each year on the anniversary of Donny’s death. Swagger gives Sarah a list of things to get, and sends her out to get them. She eventually buys everything, and he quickly instructs her how to treat his bullet wounds before passing out. Even though shes not a nurse, she does a decent job of cleaning him up. Meanwhile, Memphis looks further into the assassination attempt and discusses it with FBI agent Alourdes Galindo (Rhona Mitra), who tells him to stop looking into it. The facts don’t add up though, since there are several discrepancies with the news and Timmons story. He wants to talk with Timmons about it, but it turns out he was murdered the previous night in a “botched burglary”. Memphis goes to all of the locations that Swagger went to, and goes to the church tower where he sees specific markings in the dust. Hes convinced that Swagger isnt the guy they should be after, since he would not have missed the president and hit the Ethiopian Arch Bishop. Memphis also goes online to a gun chat room, where he finds out exactly what kind of gun was used in the assassination attempt. During this time, he begins to notice that people are watching him.

Swagger eventually gets better, and tells Sarah that hes going to go after the guys who set him up. Sarah informs him that news reports are saying that Swagger killed his dog and tried to kill the president, with pictures released of him scouting out each location. Swagger is pissed that they killed his dog and plans to see this through to the end. He blames himself for Donny’s death, but Sarah slaps him in the face and tells him that Donny fully knew what he got into. Sarah gives Swagger Donny’s first sniper rifle and volunteers to help him. Their first course of action is to find Memphis. Sarah wears a disguise and meets Memphis in a public place, handing him the photographs of Johnson’s license plate. Swagger watches across the street, but is seen by police who think that hes suspicious. Two cops approach him, one with an attack dog. After Sarah and Memphis leave, Swagger throws coffee into a cops face and makes the dog attack the cop. He then throws the cop and dog through a window while beating the crap out of the other police officer. He ditches his jacket and walks away. Memphis sneaks into a restricted area of the FBI office and tries to find information about the license plate number, but hes blocked out and requires a delta level clearance. Galindo tells him that hes going to be fired if he keeps looking into this, and starts to notice the faults as well in the facts of the Philadelphia shooting. She winds up telling him how to get the security clearance though. Dobbler informs Johnson about the internet chat room, and someone trying to access delta level security information. They realize that Memphis is looking where he shouldn’t, and plan to take him out.

As Memphis is walking on a bridge, he is abducted by masked men in a van. Memphis is severely beaten, and the men put him in a rig that will make him shoot himself. Swagger shoots each man one by one using Donny’s rifle, and frees Memphis, who knows that Swagger was set up and agrees to help him. Johnson hears that Memphis didnt die and knows that hes now working with Swagger. He orders his men to look deep into Swaggers past. Memphis drives them to Tennessee, where they visit an old humorous marksman expert. Swagger asks the expert who could make a shot beyond a mile thats still alive. Apart from Swagger, there’s one man. The sniper used to be sadistic, just shooting to wound and killing everyone who tried to help the wounded. He must have killed hundreds of people. He was in a building that was destroyed, and some believed him to be dead. The sniper is Michael Sandor, the handicapped Russian thats working with Johnson. Johnson knows that Swagger is going to look for the shooter, and so lets Sandor act as bait to lure Swagger out. Dobbler found that Swagger has sent flowers to Sarah each year, and believes that she helped him. Johnson orders them to get her.

Swagger and Memphis go to a big hardware store and buy lots of supplies. They then drive out to the woods where they make napalm, pipe-bombs, and gas bombs. Swagger teaches Memphis to use a sniper rifle, and makes him practice while he sets off bombs nearby. Meanwhile, Sarah thinks that someones in her house and takes out her shotgun. A henchman appears with a silenced pistol, but is blasted through the chest by Sarah. Payne sneaks up behind Sarah and makes her put down the shotgun. He asks her where Swagger is, and beats her up. Its heavily implied that Payne rapes Sarah. Elsewhere, Johnson meets with corrupt senator Charles Meachum (Ned Beatty) and gets his approval to fly in over twenty soldiers to kill Swagger.

Swagger and Memphis find where Sandor is, and plan an attack. Memphis remains in position near the forest while Swagger moves closer to the cabin. He sneaks up behind a guard and stabs him in the back, then sets up some bombs. He stabs another guard through the chin, and again places more bombs. Swagger makes quick work of the third guard, and shoots the fourth in the head. Sandor is all alone now, and reveals to Swagger what really happened. The president was never in any danger their only target that day was the Ethiopian Arch Bishop, because he was going to talk about Americans committing genocide to build an oil pipeline (approved by our government, since nothing happens without their approval). The best way to kill the Arch Bishop was to make it look like a failed attempt on the president. Swagger unwittingly was part of the genocide, since back in Ethiopia Donny and him were covering the soldiers that murdered the villagers. Swagger asks about Johnson, but Sandor doesn’t know what his real name is, though he does know that he works for Meachum. Soldiers surround the cabin, and Memphis warns Swagger. Sandor pulls out a pistol and shoots himself in the head. Swagger orders Memphis to set off the pipe-bombs, and then the gas bombs. Two soldiers come into the house, and Swagger shoots both dead. Memphis sets off the bombs, and Swagger shoots his way out of the cabin. Memphis covers Swagger, and a big shootout ensues. Swagger makes it to Memphis, and a helicopter shows up to kill them. Swagger thinks back to Donny’s death, and fires upon the helicopter. Both men run a safe distance and set off the napalm bombs, blowing up the remaining soldiers and destroying the helicopter. The incident is covered up though, since all the bodies were removed before the authorities showed up.

Memphis calls the FBI field office and talks to his superior officer, informing him that he has Swagger in custody. He talks long enough for them to trace the call. Swagger then calls Johnson, who tells him that he wants to meet. Johnson reveals that he has Sarah, and Swagger reveals that he recorded Sandor’s confession about everything. Johnson agrees to meet, but wants to see him coming from a long way off. Swagger requests that Meachum be present. The meeting is in the snowy mountains where Johnson, Meachum, Payne, and Sarah are present. Payne rigged a shotgun to his hand and is holding Sarah at gunpoint. They see Swagger walking towards them in the distance, and he is immediately shot in the chest by a hidden sniper. Johnson and Meachum are pleased, but their hidden snipers are shot through the head one by one. Turns out Swagger was posing as a hidden sniper while Memphis was walking towards Johnson. Memphis pulls out his armor and continues to walk towards them. Swagger aims carefully, and destroys Payne’s shotgun while blowing off his thumb. Payne laughs in shock, and then Swagger blows off his arm. Memphis disarms Johnson and Meachum, and Swagger finally approaches them. Sarah grabs a pistol and shoots Payne to death. Meachum offers Swagger a job, but he refuses. Memphis calls in the FBI to come to their location, and Swagger burns Sandor’s recording. Memphis tells him that it proves he’s innocent, but Swagger knows that whoever turns over the recording is dead. No one there is innocent, and so they wait for the FBI to show up.

Some time passes, and Swagger is brought to a meeting in the Department of Justice. Present are the Attorney General, Johnson, Memphis, and Sarah. Memphis shakes Swaggers hand and slips him unseen by others in the room. In front of him is his sniper rifle, and Swagger’s hands are freed. He asks if the rifle has been tampered with by the FBI or any other authority, but it hasn’t. He turns to Memphis, asking whether he believes in Swagger’s innocence whether he trusts him with his life. Memphis answers yes, and Swagger loads a bullet into the rifle, aims at Memphis, and pulls the trigger to a resounding “click”, as nothing happens. The truth of the situation is clear: before he left to scout locations, he removed the firing pins from all his weapons (including the rifle in front of him that was supposedly used in the shooting). It was impossible, then, that he had used his weapon to kill the Ethiopian Archbishop. Clearly innocent, Swagger and Memphis then argue that the real guilty parties in the room is Johnson, tying him to the mass grave in Ethiopia. But the Attorney General has no jurisdiction over crimes Johnson may or may not have committed in other countries. Johnson is allowed to leave, telling Swagger that he had won again. The Attorney General frees Swagger, convinced that he’s innocent.

Some time later, Johnson celebrates his victory with Meachum and Dobbler in a remote cabin. Meachum and Johnson laugh about winning again, and Meachum plans to move Johnson out of the country to fix another problem they have. As Dobbler begins to explain his next mission, blood splatters on his face. A dead guard falls down directly in front of him. Johnson realizes that Swagger is there, but is shot through the chest. He dies very painfully. Dobbler turns off the lights, and Meachum orders him to get the car. Meachum’s SUV explodes, and the men panic. Swagger moves underneath the cabin, and Dobbler tells the remaining bodyguard that Swagger is under the floor. Swagger shoots Dobbler through the knee from under the floor, and shoots the guard to death from below. He then enters the cabin, where Dobbler pleads with Swagger to spare his life since he didn’t do anything. Swagger shoots Dobbler in the chest and approaches Meachum. “I’m a Senator: You can’t do this!” cries Dobbler, as Swagger blows his brains out with a pistol, before placing it in Johnsons hands. Swagger breaks the gas line of the cabin, and as Swagger runs to his car, the cabin explodes. The film ends with Swagger, Sarah behind the wheel, driving into the distance.